The present invention relates to a gear ring pump.
Gear ring pumps are known in the art. A known gear ring pump has a housing, a hollow gear arranged rotatable in the housing and having 5-16 teeth and engaging with a pinion which is driven from a driving shaft and also has teeth which are by one tooth less than the hollow gear. The sealing between a suction space and a pressure space is performed by sliding of the teeth heads of the pinion over the teeth of the hollow gear at a location which is opposite to the location of the deepest teeth engagement, and by abutment of the driving teeth flanks of the pinion against the teeth of the hollow gear at the location of the deepest teeth engagement. The teeth heads of the pinion are freely received in the teeth gaps of the hollow gear, and the theoretical teeth shape of the pinion is determined by rolling of the pinion rolling circle over the hollow gear rolling circle. Such a tooth ring pump is known for a long time and disclosed, for example, in "Lueger Lexikon der Technik", Deutsche Verlagsanstalt, Stuttgart, Bd.7, 1965, S. 218. These pumps are identified there as "Eaton pumps". The above discribed pumps have a simple construction. The teeth of the hollow gear are generally formed as circular segments; in other words, the entire tooth contour is determined by a single circular arc. Instead of the circular arc contour it is also possible, however, to use (as well as in the present invention) another curve, for example a cycloid. A considerable problem with the above-described known Eaton-gearing is that each tooth of the hollow gear is constantly in engagement with a tooth of the pinion. This is performed in a construction in which the pinion has by only one tooth less than the hollow gear. The feature that all teeth are always in engagement causes considerable problems not only during the manufacture but also during the operation of the gearing. The manufacture must be very accurate, on the one hand. When wear takes place during the operation, the sealing between the suction space and the pressure space of the pump, particularly at a location which is opposite to the location of deepest engagement, is imperfect and the effectiveness of the pump considerably reduces. Moreover, the pump is suceptible to wear, because during the operation a very strong specific sliding between the abutting parts of the pinion teeth and the hollow gear teeth takes place. This takes place, first of all because the teeth surfaces of the hollow gear which correspond to the teeth flanks of a normal gear are relatively considerably inclined. Moreover, parts of the pinion teeth which directly transmit torque and abut against the teeth of the hollow gear, namely abut against the relatively sharply curved edges between the teeth flanks and the teeth heads are characterized by especially high hertz pressure which additionally stimulates the wear. Furthermore, the oscillation of the instantaneous supply volume over the rotary angle and thereby the supply pulsation of this pump are very high.
An additional problem of the Eaton-pump is that the individual supply means limited in radial direction by the hollow gear and the pinion, constantly change their volumes, since they are separated from one another by the multiple teeth engagement. This leads to a subdivision of the working space into individual chambers, which is undesirable also when they communicate with one another by laterally arranged pockets in the housing.
Finally, the multiple teeth engagement of the Eaton pump has the disadvantage that the real teeth engagement for the torque transmission from the pinion to the hollow gear in circumferential direction, which is under hertz pressure, is frequently remote from the position of the deepest teeth engagement because of manufacture tolerances of the teeth flanks shape of the hollow gear and of the pinion. Because of the thereby varying angle position of the pressure points between the teeth flanks of the pinion and the hollow gear, a teeth force component generated on the hollow gear tends to increase the axes distance between both gears. As a result of this, the sealing between the teeth at the location opposite to the deepest engagement becomes worse, and the thus increased teeth force is higher in dependence upon the higher supply pressure. Because of the above described reasons, the Eaton pump, despite its simple construction, is implemented in practice to only a limited extent for relatively few cases.
The disadvantages of the Eaton pumps with a teeth number difference of more than one, in which the teeth in the region opposite to the deepest teeth engagement are not in engagement, are eliminated in a construction in which in the region of the above-mentioned location a filling piece having generally the shape of a half moon or sickle is arranged so that the teeth heads of the hollow gear slide along its convex surface, whereas the teeth heads of the pinion slide along its concave surface. In such a construction there is more freedom for the teeth shape so that the teeth engagement characteristics can be favorably selected. However, these pump types are considerably more expensive than the Eaton pump because of the expenditure for the filling piece and the exact positioning and the shape of the latter.